It is cheaper but not a comparable system as in you can't replace the need for an MSE with the skyceptor. The MSE is capable of dealing with longer ranged ballistic missiles and it also has a small warhead which the stunner completely lacks. I've seen reports stating that the stunner has been designed to counter ballistic missiles with ranges up to 300km which would include only a fraction of the threats the MSE can handle. For many threats however the stunner is probably just as good but comes in supposedly at a fraction of the cost.

The two systems are intended to create a double-tiered missile defence capability. Iron Dome is intended to counter short-range rockets and 155 mm artillery shells, threats of ranges of up to 70 km range, while David's Sling will be used against medium and long-range rockets, short-range ballistic missiles and cruise missiles, dealing with ballistic threats with ranges from 40 km up to 300 km ~ Jane's Defence Weekly